It sounds like you are on the right track. You can only do so much. Don't get upset with yourself for grieving - it is perfectly normal and natural as part of life iwth a difficult child. Adopted kids go through some challenges that other kids don't - regardless of how old they were when they were adopted. I don't know why, but even kids who are adopted at birth have that same hurt inside. I have heard this from many friends who were adopted or who adopted kids. One of my high school friends adopted twin boys from another country. She met the foster parents that cared for the boys for the first 18 months of their lives. She truly thought that they would not have those hurts because they attached well to the adopted parents and then to her and her husband and other kids. They are fairly well adjusted non-difficult children and still they have voiced enough to let her know that the hurt is still there deep inside. At their ages (early elementary school) they have not read or heard about it anywhere, they are speaking from their hearts.
This may be one piece that your son needs to address and doesn't feel able or willing, or may not even know how to put it into words. Not ever therapist is able to handle adoption issues, so it may be that at some point this needs to be explored with a good therapist that he connects with.
It is really scary to wonder if your child will allow you to parent him. I know that fear. My mother helped my oldest child reject our parenting completely. he was my heart and for the first 8 or 9 years we were incredibly close except for the wedge my mother inserted. I don't think she meant to do that at the time. In your case it is his pain and the lure of the drugs that are a big part of why he is rejecting your parenting - of course that is just a guess. Until the drugs are dealt with his brain chemistry will NEVER accept "normal" life. While you may only get him to stop using drugs by finding a way to convince him that properly prescribed psychiatric medications will help with the problems he is using drugs to self medicate. The big "catch" is that until he has the right medications he won't be able to get away from the symptoms he is self-treating with drugs - but until the illegal drugs are out of his system there is NO WAY to safely prescribe the right medications to treat him. The doctors that work with him MUST know what illegal drugs he is using (even if it is "just" OTC medications like cold medications (called "skittling" in many areas) or else they may rx medications that could interact in a very dangerous way.
Sadly, at his age there is only so much you can do. I hope that you and your husband will attend narc anon or al anon, and take your easy child to alateen. Addiction is a family disease and is VERY contagious. Even those who are not addicted will acquire the behaviors and this can keep the addicted person from getting help. Having the family get help increases your difficult child's chance of successfully kicking his drug habit and staying clean - and increases it substantially. Don't pick just one meeting - go to as many as you can the first few weeks. This will help you find the meetings that you feel most comfortable in - and will increase your chances of sticking with it. Even if difficult child will not go to AA or Narcotics Anonymous, you, husband and easy child should go.
I also strongly recommend the Love and Logic books - Parenting Your Teen with Love and Logic is an amazingly helpful book for parents of difficult children. It can help with many of the things you are dealing with. L&L emphasizes using natural and logical consequences while strengthening the loving bond between parent and child. It also works very well - and is incredibly supportive of parents, in my opinion. You can learn more about L&L at their website -
www.loveandlogic.com .
Whatever you do, keep reading and posting here. We will be here when you need/want us and the group is always super supportive.